The invention relates generally to a fast switching circuit and more specifically to a fast switching circuit between two voltage levels within a dual energy x-ray system.
An x-ray baggage scanner may be used to detect the presence of an explosive device in baggage. The scanner issues an alarm if it detects the explosive device. Every false alarm requires a suspect bag to be searched by a security guard. Consequently, it is important to develop scanners that keep the number of false alarms as low as possible. This ensures low operating costs and maximum baggage throughput. One type of technique used in the x-ray baggage scanner is a technique called material decomposition. Material decomposition allows the effective atomic number of material to be measured when the baggage is scanned by the baggage scanner. An explosive material is generally characterized by a relatively high atomic number and is therefore easy to detect by material decomposition.
Material decomposition involves measuring an x-ray absorption characteristic of a material for two different energy levels of x-rays. Alternating beam type is one type of scanner, which generates two different energy levels of x-rays. However, the two energy levels generated by this scanner are not much different from each other. Thus, accurate analysis of the atomic number of the object being scanned is not possible. Dual detector type is another type of scanner, which generates two different energy levels. However, this scanner also doesn't produce two significantly different energy levels and further needs two detector arrays rather than a single detector array.
Two different energy levels of x-rays can also be generated by applying two different voltage levels to the x-ray source. In this case, a power supply supplies two different voltages changing rapidly between two different high voltage levels to the x-ray source. However, the power supplies currently used for the x-ray source have a slow time response due to a cable capacitance of a cable between the power supply and the x-ray source. Therefore, it would be desirable to design a fast switching circuit that would address the foregoing issues.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.